The moment you have any database or filesystem or remote-service, the hybridization starts anyway.
Sure, technically a single computer's local RAM is being managed with strict guidelines, but that correlates less and less to overall application state and behavior these days.
The promise of FRP was to solve this problem. It makes "state change" a first class object, and organizes your code around it.
The problem is that nobody made an usable FRP system yet. It's not obvious why it's so hard, and everything feels like it should be easy. But everybody just keep failing.
Knowing that a small collection of functions is not referentially transparent is better than having to deal with any part of the program potentially changing your state.
Sure, technically a single computer's local RAM is being managed with strict guidelines, but that correlates less and less to overall application state and behavior these days.